Ok I'm hearing a lot of conjecture, and people are STILL blowing money on shitty rotors, so I will tell you all why blank rotors are better.

The reason for the creation of cross drilled rotors initially was to remove the "gasses" from the brake pads. HOWEVER, most of your modern brake pads (Axxis metal, AEM semi-ceramic) do NOT produce gasses when heating. This was on bad brake pads used in the 1950s and 1960s. Back then, asbestos was also used, and we dont use that either.

The other reason is so called heat dissapation. I don't have my physics and thermo books with me, but the logic is that the holes in the rotor are suppose to allow the brake pad to cool. So...air gets into the rotor from the inside of the vents. If you have a back rotor which is solid, air gets into these holes how? If your stopped, you are leaving air inside these holes sandwiched between the pads, thus creating air with a rising temperature. Its increasing in pressure from the heat, which I guess you "could" call a gas that would affect braking. So the cross drilled rotors do not remove any gasses formed by brake pads (because there are none created anymore) but could possibly inhibit the creation of "hot spots".

Cross drilled rotors have LESS contact area because of the holes.
But if the rotor is cooler, its better, right? Well no, because these rotors are not cooler. THe heat is generated from the pad/rotor contact. What removes heat the most effectively? When stopped or moving, the pad transfers heat into the rotor because its made of cast iron. the rotor has a lot of surface area and even vanes in it. But the little holes allow air in this surface contact, and you can transfer more heat into a solid big *** chunk of cast iron more than you can into the air. Don't believe me? Touch some steam at 150 degrees, then touch a piece of hot metal which is at 150 degrees. Which burns your hand? the metal. So let the heat transfer into the metal, because since it has so much more surface area, dissapates better.

Companies that sell cross drilled rotors that are redrilled may not be structurally sound. I have actually seen pictures of rear Integra rotors that have had hairline cracks turn into the rotor actually breaking apart!

Do your homework. Even Porsche and Ferrari will admit that the cross drilled rotors they use are for looks. So if you are one of those kids who thinks the little holes look cool, get a name brand drilled rotor like Ferrari does. The REASON Ferrari's 'holed' rotors are alright to use is because they are CAST with the holes in them, so they are not actually drilled into cast iron rotors. Cheap drilled rotors are not safe, and even the good ones are not necessary. Why do Ferrari do it? People THINK they want it, and it sells. If you don't believe me, go into the business world. You will learn that pretty soon, you can sell utter **** if people THINK its better.

Simply stated, the function of any vehicles brake system is to stop the vehicle. This is accomplished by absorbing the kinetic energy stored in the moving vehicle, and converting it into heat. The friction caused by the brake pad rubbing on the rotor is the source of this heat. The more quickly and efficiently that heat can be absorbed and dissipated, the more quickly and efficiently the car will stop.

There are several contributing factors to this heat reduction. One of the most common sources of heat is from the gases produced by the bonding agents of the brake pad burning off. Under severe braking, this can actually produce a boundary layer of gas that pushes the pad away from the rotor, which can lead to excessive brake fade. The cross-drilled holes or slots in a rotor provide an escape path for these gasses (de-gassing or out-gassing are common terms), and allow the pad to stay in contact with the rotor. As well as de-gassing, cross drilling or slotting will provide better wet weather braking as water is swept through the holes, or down the slots.

A vented rotor can be viewed as an air fan. When in motion, the vents draw air from the center of the rotor outward. This air flow, over an increased internal surface area, effectively dissipates rotor heat. Cross drilling adds to this air flow, as well as providing additional rotor surface cooling. "

This company is just telling you that the rotors may be cooler, however they fail to mention that the holes really do create a more than substantial decrease in surface area, thus less braking, thus less heat created, thus the less heat CREATED will leave the rotors cooler, the holes barely do anything! Its the less braking lowering the temperature!

Slotted rotors-
Find me a company that uses stock slotted rotors. They remove brake dust, but if you study braking systems, you find that with modern cars, flat blank rotors and semi-ceramic pads, the brake dust causing the rotor to slip on it is almost non-existent. But the brake dust doesnt need all those lines. Notice how most front brake pads (and most back) have that line down the middle to give essentially two bite points. If OEM or racing companies found it to be a benefit, they would do it.

PROOF OF IT ALL:

Find me an F1 car as of now that uses cross drilled or slotted rotors.
They all use full ceramic rotors and ceramic pads. Are they drilled or slotted? No.

If they helped the fastest cars in the world, wouldn't they use them? Its basic calculations that show the lack in surface area does not make up for the possible loss in temperarure. They use brake cooling air ducts insted.

BIG BRAKE KITS:
Some have asked if the big brake kits are worth it. This is sort of a relative question, but the simple answer is no. Regarding the big ones with drilled rotors, if you know that they are cast that way, at least they wont crack. I will still advice against them.
In terms of a big brake kit, I have seen some for Civic DX models. Civics have the small pad, small caliper, and a 9.5" rotor. The big rotors are 12" in diameter, ok so the overall diameter is close to that of an Acura RL (1999). But the sweeping area (the area that the pad can grab) is still the same if they use the same caliper and same pad. If you have the same pad and caliper, you are using the same rotor surface, just farther out, so it will increase braking from stock. However, if you were to change knuckles, etc, and get Acura RL caliper (larger piston than your civic DX piston), RL pads (much bigger and taller), and RL rotors 11.8" but much more surface area is touched, then you have a better brake setup because you have OEM parts, and a better grip on more area of the rotor. The downfall is added weight (since big brake kits are usually 2 piece and lighter) but the benefit is that you have so much more stopping. Ok, so the big brake kit will have less unsprung and rotational mass (so a little better accelleration but less braking), but they tend to run over a grand, and you can use OEM parts to build a better setup for half that.

IN CONCLUSION:
Don't buy slotted or cross drilled rotors, blank are better, and stop better. Physics people, get me my formulas and help me out here.

If you must get rotors with designs on them, get the slotted ones by a good company, and DON'T get blank rotors redrilled with little holes all over them. IF you absolutly must have the rotors with holes cause you like em, get them from a company that casts the rotors like that. I have seen rotors break and this is for your safety!

REMEMBER......
Your car will only stop as fast as your tires will allow. All the braking in the world wont work if your tires are bald and on ice!!

I'm a blank fan, but must set the record straight on a couple notes. First is that the reduced area argument doesn't work, because friction force is independent of surface area, it's not even in the equation: F = u*N where u (mu) is the coefficient of friction, and N is the normal force on the object.

Second, one of the big reasons F1 cars don't have holes or slots or anything is because they're made of carbon, which is a ceramic. Ceramics (like glass) are characterized by being extremely brittle, most notably in tension. Their maximum tensile stress is usually less than 10% of their maximum compressive stress. Any holes or irregularities will cause stress risers that they cannot withstand, and they will shatter. Iron has the advantage of being quite ductile, and so can tolerate these stresses better, although as we've seen, not indefinitely. The reason they are chosen for F1 cars is because they retain their extreme hardness and strength at very high temperatures, and exhibit low thermal expansion and conductivity.

I have autozone blanks, and always will, but just wanted to make sure we were all on the same page.

I don't know whether slotted rotors dissipate heat or not, but they perform better in the wet possibly because they evacuate the water better. I'm not going to sit here and state that as a fact because that's something that needs to be tested scientifically. Just in my personal experience, I will say they perform better in the wet. However I don't recommend stock sized slotted rotors because of the loss of surface area and the loss of metal in the rotor.

*** edit
Holy **** I forgot my whole point in posting

I like slotted rotors because they keep the pads fresh. They scrape off a tiny bit of the top layer so they dont get glazed over. I like the feeling of the pads after they've been broken in properly. They don't have the same bite after you've put some miles on them on the street.
***

Cross drilled I can't say. I've driven a car before and after, and didn't feel anything strong enough to make a decision. I don't use them on my car. If you use them on yours, you need to use a larger than factory sized rotor to make up for the loss in surface area and also to account for the abuse that you'll be putting the braking system through. If you buy quality rotors, larger than your stock size, and you don't overheat them and then sit on the brakes for a long period of time like at the end of a freeway offramp, you wont crack them. They use them stock on a lot of motorcycles.

I agree with the original post that modifying existing rotors is a bad idea. If you buy slotted, crossdrilled, or both rotors, make sure they were cast that way.

The best rotors come from DBA. They have a special venting system they call "kangaroo paw".

Rotors don't seem to affect braking performance all that much until you get the brakes nice and hot. Then, smaller, thinner rotors with less surface area will tend to fade, increasing your braking distance a great deal from when the brakes were cool. Pads have the biggest effect.

Tires usually mean better braking, sometimes not. It depends which has reached its max potential, the tires or the brakes. On those shitty *** lifetime warranty pads, the braking system is most likely your weakest link. In this situation, using better tires wont effect your braking distance.

On my EG I have LS knuckles front and rear, a Wilwood adjustable proportioning **** set up so the front lock up just a split second before the rear, braided lines, a 91 Si 15/16 master cylinder, axxis metalmaster pads front/rear, brembo blanks front/rear, and super blue ATE brake fluid (lasts forever). I removed the "mud guards" from each corner and my rims allow pretty good airflow over the rotors. I could never ask for better braking. On good tires with a good surface, I could probably throw you out of my windshield. Haven't tried it. Sometimes I use slotted. Unfortunately the price is more than double.

LOL, that is also true, but has nothing to do with friction force. Try reading up a little more and you'll see what I'm talking about. Key words: coefficient of friction, normal force, static, kinetic...

And once again I'll point out that the formula has nothing to do with pressure, because it has nothing to do with area. Only the normal force on the object. I wish it weren't so, but tis true.

Also, Pressure = Force/Area, this is our key. less area. The force of pressing the pedal is the same, bus ditributed over less metal, thus more pressure.

Why do more powerful cars use larger brake pads? more surface. The holes reduce the area, same theory as switching to a smaller rotor.

friction force is mu*N. while the magnitude of a theoretical friction force is independent of the areas of contact, in the real world contact area matters. Due to irregularities on the surfaces in contact with one another, a single point of contact can generate a force vector of certain magnitude and direction for a given amount of time before the dynamic characteristics of the motion in quesiton change the properties of said vector. having more points doing the same ensures that if some of the points lose contact, grip is maintained. it's fairly complex, way beyond my abilities to really explain .

what is also being left out of this discussion is the rotor's function as a heat sink. If we consider the brakes as a thermodynamic system converting kinetic energy to heat energy, we will see that the heat created by friction has to go somewhere. that somewhere is generally the rotor, since it is made from a material that conducts heat. Given the size and shape of the rotor, the rotor has a certain heat capacity--when the rotor can no longer absorb more heat, it begins to go somewhere else, like the calipers and the fluid, which leads to fade. What slots or x-drilled rotors do is remove matter from the rotor, lowering the effective heat capacity. It may aid in quicker cooling, but that's not always what's wanted--especially when you could cool quicker and maintain a higher heat capacity with blank rotors and some ducting. you can look at it like fighting a fire with a small cup or a bigger bucket. sure, it takes less time to fill the cup, but the bucket's going to be more effective.

And yes, it is true that pure friction force from the coefficient of friction is the theoretical way, it's not 100% true. Tire grip is the best example of this, the mechanical interlock between the tire and the road surface can be thought of as velcro in shear. More velcro = more force required to slip the 2 pieces together. From what I have seen though, brakes are usually regarded as pure friction, as it's easier for calculations.

Another interesting thing is something that came up in a discussion with Mark Ortiz. I mentioned water cooling brakes by spraying the rotor with a water mist, and asked The Right Way to do it, as there is probably also a Wrong Way. He pointed out that the rotor is heated where it contacts the pad, and cools along it's trip around as it rotates. Cooling the rotor too much on the non-pad part of it's trip can induce thermal stress and cracking. The 2 sections of the rotor cannot be too different in temperature, or Bad Things begin to happen.

the best cooling method would probably be using air scoops, or some guy in the ITR forum did a DIY on running ducting from the front of the car to inside the vents of the rotors. I suppose you could water cool the caliper bodies, although i dont see that in any racing, so i dont see how effective it would be. i mean you want them to be somewhat hot.

The idea is to cool the rotor. The water should be sprayed in a fine mist on the inner part of the rotor by the leading edge of the pad. This has been used in a few applications, as well as water cooled calipers. I forget the name of the system, but there is a method of continually returning the fluid to the master cylinder from the calipers on a separate line. This way, your brakes are self bleeding, and get a supply of cool(ish) fluid whenever you use them.

From what I have seen though, brakes are usually regarded as pure friction, as it's easier for calculations.

Brakes are always 'pure' friction. I'm not sure what 'non-pure' friction would be??

It's more accurate to say they're usually regarded as being linear. When the friction coefficient is not constant, then the friction is non-linear. That's really what this is all about. Mu can be a function of pressure, temperature, velocity, or phase of the moon. For brake pads it's probably a weak function of pressure & temperature, becoming a stronger function of temperature once a certain (really hot) temperature is exceeded. It's a very weak function of velocity, as long as the velocity is not near zero.

Mu of elastomer materials is notoriously non-linear. That's tires in contact with the road...

That's a better way of putting it, thank you. By pure friction, I was differentiating that from tire-like friction, which isn't just a function of the friction coefficient of the materials, but also of the mechanical interlocking of the materials and the modulus of elasticity of the tires when ripping them through the small holes in the road.

When I'm on the track, sometimes it seems like the friction of my brake pads really is a function of the phase of the moon.

I'm a mechanic at Les Schwab tires and I can tell you from experience that selling Power Slots seem to have a huge advantage over oem. Maybe not so much in our needs on lighter cars such as Hondas, but I can sure tell you have have seen shitloads of women in their huge *** SUVs warping rotors all day long. Slap some Powerslots on there and they never come back. Only experience I have but just my 2 cents

I'm a blank fan, but must set the record straight on a couple notes. First is that the reduced area argument doesn't work, because friction force is independent of surface area, it's not even in the equation: F = u*N where u (mu) is the coefficient of friction, and N is the normal force on the object.

The problem with this relationship is that it is a gross approximation used to greatly simplify the math. It may be a decent approximation over limited ranges of normal force for some materials. But it should not be looked at as a physical law. Rather, it is just a mathematical model that is only somewhat true in some situations and perhaps good enough for rough approximationss. If it was true all the time, then running 205s would be no better than running 175s since normal force and friction coefficient are the same (assuming the same material is used on both tires). And we all know that's not true.